For a driver of a vehicle, or in general for vehicle occupants, the appreciation of an emergency vehicle (EV) sounding a siren signal is difficult and depends on many factors. These factors include wideband noise sources that are present in the vehicle environment, such as air conditioning, engine noise, road/tire and wind noise.
Additionally, movements of EVs, when going to an accident place or leaving it, involve for a listener (in a “sensing vehicle”) a modification of perceived siren signal frequencies due to Doppler effect. When an EV is approaching the sensing vehicle, the perceived siren signal has a higher pitch, and when the EV is receding from the sensing vehicle, the perceived siren signal has a lower pitch than a pitch in a static EV case.
Due to these factors, it is difficult for a driver to recognize and localize an EV, and often the driver only recognizes and localizes an EV in close vicinity and definitely when he sees it.
In the prior art, basically a single frequency detection is used for EV recognition which is not robust.